The present invention is directed to star-couplers in which a plurality of optical fibers are connected together. The invention is also directed to methods for making the couplers.
Data transmission over optical fibers offers many significant advantages compared with metallic conductors, including: long distance transmission without the need for repeaters, immunity from electromagnetic interference, cross-talk and ground loop, high bandwidth capabilities, small size and weight, high degree of intercept security and dielectric isolation, and long term cost reduction. These desirable features of optical fibers have strongly stimulated efforts both in fiber optics and in supporting technologies such as fiber optic coupling.
Fiber optic couplers provide for feeding and tapping of optical energy. Fiber optic couplers are widely used in multi-terminal communication systems and data buses. In these applications, a common optical path provides communication among a plurality of terminals. Typically, each terminal communicates to every other terminal and provides information on a time shared basis. The effectiveness of such systems depends on characteristics of the optical fibers themselves as well as on the coupling devices employed to share and distribute information.
A star-coupler is a device which distributes the power on any one of several incoming channels to every one of its outgoing channels. Star-couplers are intended to have minimal insertion losses and a substantially uniform power distribution over the outgoing channels. Thus, a system employing a star-coupler and a plurality of terminals represents a parallel distribution system.
Star couplers are particularly useful in the field of optical communications for coupling together a plurality of optic fibers to form a network. Several different starcouplers are known. In general, the couplers have a plurality of incoming channels, a plurality of outgoing channels and a mixing zone which couples optical signals from any one of the incoming channels to all of the outgoing channels. The mixing zone may comprise optic fibers which are tapered and fused together or wave guides in solid blocks of glass. These glass blocks usually have wave guides specially prepared by ion exchange processes or otherwise, and the fibers are aligned with the wave guides. The incoming and outgoing channels are typically bundles of optical fibers. Information in the form of light pulses as signals from any single optical fiber of the input fiber optic bundle is transmitted via the coupler to each of the optical fibers in the output fiber; optic bundle. Illustrative patents describing these structures include U.S. Pat. Nos. 4,291,940, 4,362,357, 4,449,783, 4,484,794, 4,590,619 and 4,653,845.
Unfortunately, the above-mentioned type of star-couplers are generally costly and difficult to construct.